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HitTestResultCallback Delegate

Represents a callback that is used to customize hit testing. WPF invokes the HitTestResultCallback to report hit test intersections to the user.

Namespace:  System.Windows.Media
Assembly:  PresentationCore (in PresentationCore.dll)

public delegate HitTestResultBehavior HitTestResultCallback(
	HitTestResult result
)
In XAML, you can use delegates but you cannot define your own.

Parameters

result
Type: System.Windows.Media.HitTestResult

The HitTestResult value that represents a visual object that is returned from a hit test.

The hit test callback method defines the actions that you perform when a hit test is identified on a particular visual object in the visual tree. After you perform the actions, your callback is expected to return a HitTestResultBehavior value that determines whether to continue iterating through the visual tree for any other visual objects.

The following example shows how to invoke HitTest by using a HitTestResultCallback value. The corresponding hit test callback method is also defined.

// Capture the mouse event and hit test the coordinate point value against 
// the child visual objects. 
void MyVisualHost_MouseLeftButtonUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
{
    // Retreive the coordinates of the mouse button event.
    System.Windows.Point pt = e.GetPosition((UIElement)sender);

    // Initiate the hit test by setting up a hit test result callback method.
    VisualTreeHelper.HitTest(this, null, new HitTestResultCallback(myCallback), new PointHitTestParameters(pt));
}

// If a child visual object is hit, toggle its opacity to visually indicate a hit. 
public HitTestResultBehavior myCallback(HitTestResult result)
{
    if (result.VisualHit.GetType() == typeof(DrawingVisual))
    {
        if (((DrawingVisual)result.VisualHit).Opacity == 1.0)
        {
            ((DrawingVisual)result.VisualHit).Opacity = 0.4;
        }
        else
        {
            ((DrawingVisual)result.VisualHit).Opacity = 1.0;
        }
    }

    // Stop the hit test enumeration of objects in the visual tree. 
    return HitTestResultBehavior.Stop;
}

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0

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